Rectennas—active antennas containing rectification devices—have been investigated in the microwave region for power transmission and detection over the past half century [W. C. Brown, “The History of Power Transmission by Radio Waves,” IEEE Trans. Microwave Theory and Techn., Vol. 32, No. 9, pp. 1230-1242, September 1984.]. Applications have included long distance power beaming [N. Shinohara, H. Matsumoto, “Experimental Study of Large Rectenna Array for Microwave Energy Transmission,” IEEE Trans. Microwave Theory and Techn., Vol. 46, No. 3, pp. 261-267, March 1998; S. S. Bharj, R. Camisa, S. Grober, F. Wosniak, E. Pendleton, “High-Efficiency C-band 1000-Element Rectenna Array for Microwave Powered Applications,” IEEE International Microwave Symposium Digest, pp. 301-303, June 1992; J. O. McSpadden, 1. Fan, K. Chang, “A High Conversion Efficiency 5.8-GHz Rectenna,” IEEE International Microwave Symposium Digest, pp. 547-550, June 1982.], signal detection [R. H. Rasshofer, M. o. Thieme, E. M. Biebl, “Circularly Polarized Millimeter-Wave Rectenna on Silicon Substrate,” IEEE Trans. Microwave Theory and Techn., Vol. 46, No. 5, pp. 715-718, May 1998.] and wireless control systems [L. W. Epp, A. R. Khan, H. K. Smith, R. P Smith, “A Compact Dual-polarized 8.51-GHz Rectenna for High-Voltage (50 V) Actuator Applications,” IEEE Trans. Microwave Theory and Techn., Vol. 48, No. 1, pp. 111-120, January 2000.]. The first receiving device for efficient reception and rectification of microwave power was developed in the early 1960's at Raytheon, based on a half-wave dipole antenna with a balanced bridge or single semiconductor diode placed above a reflecting plane.
An attraction for rectenna technology is its high theoretical conversion efficiency—roughly 95%. The greatest conversion efficiency ever recorded by a rectenna element occurred in 1977 by Brown, Raytheon Company. Using a GaAs—Pt Schottky barrier diode, a 90.6% conversion efficiency was recorded with an input microwave-power level of 8 W. Conversion efficiencies in the range of 80% are typical, with representative circuits shown below.
The concept is arbitrarily scaleable, and the optical rectenna is a direct extension to shorter wavelengths. Some of recent work in the area was performed by ITN energy systems under DOE and DARPA sponsorship “BROADBAND OPTICAL RECTENNA FOR ENERGY HARVESTING”, CECOM ENERGY HARVESTING PROGRAM Slides, Apr. 14, 2000). Such micro- and nano-scale rectenna devices can convert ambient electromagnetic radiation (i.e. solar spectrum, blackbody radiators, active emitters) to DC electric power. The potential is to convert over 85% of the sun's energy to useable power compared to ˜30% now achievable with conventional semiconductor based photovoltaics. Such devices may also be applicable to uncooled infrared detectors.
While the concept has been proven in principal, useful power conversion in the optical frequency range is prevented by the low frequency response of the planar diodes employed.
Thus there remains a need for optical rectennas having desirable frequency response and power conversion.